Number employed in the theatre (11)
I believe the answer is:
anaesthetic
'number' is the definition.
(something which 'numbs' you)
'employed in the theatre' is the wordplay.
I cannot really understand how this works, but
an anagram of 'the' is 'het' which is located in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for anaesthetic that I've seen before include "Numbing substance" , "Knockout drug" , "Number of bodies - can hesitate (anag)" , "puts people in theatre to sleep" , "Theatre number" .)